A briefly winter deciduous tree native to the American Southwest and northern Mexico, desert willow (Chilopsis linearis) produces pink flowers on its branches in late spring and summer. It needs a fast-draining soil and matures anywhere from 15 to 30 tall and wide depending on growing environment. Grow desert willow where winters are cool and dry in U.S. Department of Agriculture hardiness zones 7 through 11.
Literature on desert willow confusingly describes it as either fast, rapid, moderate or average in its growth rate. Based on written discussion of this species by Pima County Extension Service, "Sunset Western Garden Book," and Trees USA's website, growth rate of this tree is affected by the amount of water it receives. Moreover, trees that receive more water during the growing season mature to a taller and wide mature size.
Extent of Annual Growth
New growth occurs at branch tips on the desert willow and occurs in spring. Utah State University Extension includes this tree in a list of "moderate growth rate." This equates to 12 to 24 inches of growth per year. "Sunset Western Garden Book" states that when a young sapling, the growth rate is fastest, up to 3 feet per year, and then tends to slow once the tree is established. Interestingly, if desert willow plants are pruned back to 6-inch stumps in late winter and allowed to rejuvenate, the subsequent regrowth by that following fall measures 3 to 10 feet, according to the Trees USA website.
Providing light, infrequent irrigation to a desert willow increases its growth rate and amount of foliage and flowers. Highly drought tolerant, this tree responds well to irrigation and fertilizer that occurs as part of the garden landscape in suburban areas, as long as the soil is well-drained. Trees USA recommends planting desert willow in raised beds or on an elevated slope in regions where more than 30 inches of natural rains occur annually.
Trees USA states supplemental irrigation of newly planted desert willows is needed to get the root system growing and established. Well-formed root systems promote better growth as well as attain a more attractive habit and produce more attractive flowers. Trees USA's recommendation is to irrigate young trees one to three times a week, supplying 2 gallons of water to the root ball for every inch of tree trunk diameter. Applying a 2-inch layer of organic mulch no closer than 12 inches from the trunk reduces weed and turfgrass competition, hastening tree root establishment. Extend the mulch 3 to 5 feet beyond the reach of branch tips.
Over-watering the desert willow tree to promote faster and lusher growth is the biggest concern, as soggy soil conditions kill the plant. Besides natural rainfall, irregular but deep watering of an established desert willow is best. Once leaf drop starts in fall, irrigation is cut off and only natural desert rains sustain the tree until the spring when new leaves emerge, according to Trees USA. Trees planted and growing less than seven years in the ground should be given irrigation in winter every six weeks and in inconsistent frequencies every two to three weeks during warm summer months.